Fiber optic cable systems and methods to prevent hydrogen ingress

ABSTRACT

Purging interior regions of a cable reduces or prevents hydrogen darkening of an optical fiber located in the cable. While hydrogen may permeate through an outer surface of the cable, fluid circulating through the cable purges the hydrogen from within the cable. This circulation of the fluid occurs between an inner tube containing the fiber and an outer tube surrounding the inner tube.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/139,973 filed Jun. 16, 2008, now U.S. Pat. No. 7,646,953 which is acontinuation-in-part of U.S. patent application Ser. No. 11/397,791filed Apr. 4, 2006, now U.S. Pat. No. 7,424,190 issued Sep. 9, 2008,which is a continuation of U.S. patent application Ser. No. 10/422,396filed Apr. 24, 2003, now U.S. Pat. No. 7,024,081 issued Apr. 4, 2006.Each of the aforementioned related patent applications are hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention generally relate to fiber optic cablesystems for use in harsh environments such as gas and oil wellboreapplications.

2. Background of the Related Art

With advancements in the area of fiber optic sensors for use in harshenvironments, there is an increasing need for fiber optic cablescompatible with the harsh environmental conditions present in oil andgas wellbore applications. For example, fiber optic cables utilized insensing applications within the wellbore must be able to operatereliably in conditions that may include temperatures in excess of 300degrees Celsius, static pressures in excess of 138,000 kilopascal (kPa),vibration, corrosive chemistry and the presence of high partialpressures of hydrogen. The hydrogen tends to darken waveguides in thecable causing undesired attenuation.

FIG. 7 depicts one example of a conventional fiber optic cable 700suitable for use in harsh environments such as oil and gas wellboreapplications. The fiber optic cable 700, shown in FIG. 7, includes afiber in metal tube (FIMT) core 702 surrounded by an outer protectivesleeve 704. The FIMT core 702 includes an inner tube 706 surrounding oneor more optical fibers 708. Three optical fibers 708 are shown disposedwithin the inner tube 706 in the embodiment of FIG. 7. A filler material710 is disposed in the inner tube 706 to fill the void spaces notoccupied by the optical fibers 708. The filler material 710 may alsoinclude a hydrogen absorbing/scavenging material to minimize the effectsof hydrogen on the optical performance of the fiber 708. The outerprotective sleeve 704 includes a buffer material 712 and an outer tube714. The buffer material 712 provides a mechanical link between theinner tube 706 and the outer tube 714 to prevent the inner tube 706 fromsliding within the outer tube 714. Additionally, the buffer material 712keeps the inner tube 706 generally centered within the outer tube 714and protects the inner tube 706 and coatings formed thereon from damagedue to vibrating against the outer tube 714.

At least one of the inner or outer surfaces of the inner tube 706 iscoated or plated with a low hydrogen permeability material 716 tominimize hydrogen diffusion into an area around the optical fibers 708.As temperature increases, materials (e.g., the low hydrogen permeabilitymaterial 716) of prior cables disposed around optical waveguides toprovide hydrogen blocking become less effective since hydrogen diffusesfaster through these materials. This susceptibility of the opticalwaveguides to attack by hydrogen in high temperature environmentsreduces service life of the cables.

Therefore, there exists a need for improved fiber optic cables andmethods for use in harsh environments.

SUMMARY OF THE INVENTION

In one embodiment, a method of deploying an optic cable includesproviding the cable which includes an inner tube having an optical fiberdisposed inside the inner tube and an outer tube with an inner diametersized for relative retention of the inner tube disposed inside the outertube. In addition, the method includes positioning the cable at alocation. Controlled flowing of a fluid between the inner and outertubes removes hydrogen from within the cable positioned at the location.

For one embodiment, an optic cable system includes a cable and a sourceof fluid. The cable includes an inner tube having an optical fiberdisposed inside the inner tube and an outer tube with an inner diametersized for relative retention of the inner tube disposed inside the outertube. A flow path disposed between the inner and outer tubes extendsacross a length of the cable and includes an inlet and an outlet. Thesource of fluid couples to the inlet of the flow path with the fluidbeing pressurized to achieve controlled fluid flow of the fluid throughthe flow path from the inlet toward the outlet that is defined.

According to one embodiment, a method of deploying an optic cableincludes providing the cable, which includes an inner tube having anoptical fiber disposed inside the inner tube and an outer tube with aninner diameter sized for relative retention of the inner tube disposedinside the outer tube. The method additionally includes lowering thecable into a wellbore. Removing hydrogen from within the cable whilelocated in the wellbore occurs by circulating a fluid between the innerand outer tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description of the invention, briefly summarizedabove, may be had by reference to the embodiments thereof that areillustrated in the appended drawings. It is to be noted, however, thatthe appended drawings illustrate only typical embodiments of thisinvention and are therefore not to be considered limiting of its scope,for the invention may admit to other equally effective embodiments.

FIG. 1 is a cross sectional view of one embodiment of a fiber opticcable suitable for use in oil and gas wellbore applications;

FIG. 2 is a partial sectional side view of the optic cable of FIG. 1;

FIGS. 3A-E are cross sectional views of alternative embodiments of afiber optic cable suitable for use in oil and gas wellbore applications;

FIG. 4 is a cross sectional view of another embodiment of a fiber opticcable suitable for use in oil and gas wellbore applications;

FIG. 5 flow diagram of one embodiment of a method for fabricating afiber optic cable suitable for use in oil and gas wellbore applications;

FIG. 6 is a simplified schematic of one embodiment of a fiber opticcable assembly line; and

FIG. 7 depicts one example of a conventional fiber optic cable suitablefor use in oil and gas wellbore applications.

FIG. 8 is a cross sectional diagrammatic view a wellbore with the fiberoptic cable shown in FIG. 3D disposed in the wellbore and coupled to apump for circulating fluid within the cable around an inner tubesurrounding optical fibers of the cable.

FIG. 9 is an enlarged sectional view taken at 9 in FIG. 8.

FIG. 10 is a cross sectional view of a fiber optic cable as shown inFIG. 3C with addition of flow tubes between inner and outer tubes.

FIG. 11 is a cross sectional view of a fiber optic cable with annularflow paths.

FIG. 12 is a cross sectional view of the fiber optic cable shown in FIG.11 taken across line 12-12.

FIG. 13 is a cross sectional view of a fiber optic cable having an outertube surrounding a body having embedded therein one or more flow tubesand one or more tubes with fibers inside.

FIG. 14 is a cross sectional view of a fiber optic cable formed by anouter tube surrounding one or more flow tubes stranded with one or moretubes with fibers inside.

To facilitate understanding, identical reference numerals have beenused, wherever possible, to designate identical elements that are commonto the figures.

DETAILED DESCRIPTION

Embodiments of the invention relate to reducing or preventing hydrogendarkening of an optical fiber located in a cable. While hydrogen maypermeate through an outer surface of the cable, fluid circulatingthrough the cable purges the hydrogen from within the cable. Thiscirculation of the fluid occurs between an inner tube containing thefiber and an outer tube surrounding the inner tube.

FIG. 1 shows one embodiment of a fiber optic cable 100 suitable for usein oil and gas wellbore applications. The cable 100 comprises a fiber inmetal tube (FIMT) core 102 disposed in a protective outer tube 104. TheFIMT 102 comprises an inner tube 106 surrounding one or more opticalfibers 108, three of which are shown in the embodiment depicted in FIG.1.

The inner tube 106 is fabricated from a corrosion resistant material.Examples of suitable corrosion resistant metal alloys include, but arenot limited to, 304 stainless steel, 316 stainless steel, INCONEL® 625and INCOLOY® 825, among others. Examples of suitable plastics include,but are not limited to fluoropolymers, ethylene-chlorotrifluoroethylene,fluoroethylenepropylene, polyvinylidene fluoride, polyvinylchoride,HALAR®, TEFLON® and TEFZEL®, among others. The diameter of the innertube 106 may be in the range of about 1.1 to about 2.6 millimeters (mm),and in an exemplary embodiment of the invention is about 2.4 mm.Although the inner tube 106 is described as being about 1.1 to about 2.6mm in diameter, the diameter of the inner tube 106 may vary, dependingupon the materials used and the number of optical fibers 108 to beplaced in the inner tube 106.

In one embodiment, the inner tube 106 has a wall thickness suitable fora seam welding process utilized to fabricate the tube from a coil ofmetal strip. For example, the wall thickness of the 304 stainless steelinner tube 106 may be about 0.2 mm to facilitate a continuous laser weldduring a tube forming process. In another embodiment, the inner tube 106has a wall thickness suitable for fabrication by plastic extrusion.

An optional plated barrier coating 110 may be disposed on at least oneof the inner or outer surfaces of the inner tube wall. The barriercoating 110 may be coated, plated or otherwise adhered to the inner tube106 and may be comprised of a low hydrogen permeability material, suchas tin, gold, carbon, or other suitable material. The thickness of thebarrier coating 110 is selected to slow the diffusion of hydrogen intothe center of the inner tube 106 driven by a high partial pressurehydrogen environment present in some wells. Depending upon the barriercoating material, the coating thickness may be in the range of about 0.1to about 30 microns or thicker. For example, a carbon barrier coating110 may have a thickness of about 0.1 microns, while a tin barriercoating 110 may have a thickness of approximately 13 microns. In oneembodiment, the barrier coating 110 includes a nickel seed layerdisposed on the tube surface that provides an adhesion layer for anouter layer of low hydrogen permeability material. In applications wherehigh partial pressures of hydrogen are not expected, the barrier coating110 may be omitted.

In one embodiment, a protective outer coating 112 is disposed over thebarrier coating 110. The outer coating 112 is a protective layer ofhard, scratch resistant material, such as nickel or a polymer such aspolyamide, among others, that substantially prevents the barrier coating110 from damage from contact with the outer tube 104. The outer coating112 may have a thickness in the range of about 0.5 to about 15 microns,depending on the selected material.

A filler material 114 is disposed in the inner tube 106 andsubstantially fills the void spaces within the inner tube 106surrounding the optical fibers 108 to support and prevent the opticalfibers 108 from moving excessively within the inner tube 106. The fillermaterial 114 has sufficient viscosity to resist the shear forces appliedto it as a result of the weight of the optical fiber 108 when disposedin a vertical well installation at elevated temperatures, therebysupporting the optical fibers 108 without subjecting the fibers to thestrain of their weight. The filler material 114 has an operatingtemperature range of about 10 to about 200 degrees Celsius. However, thecable 100 may be utilized over a wider temperature range.

The filler material 114 is also configured to allow the optical fibers108 to relax and straighten with respect to the inner tube 106 due todifferences in the coefficients of thermal expansion between the opticalfiber 108 and the inner tube 106 and during spooling, deployment and useof the cable 100. The filler material 114 also prevents chaffing of thecoatings on the optical fibers 108 as a result of bending action duringinstallation and vibration of the cable 100. The filler material 114also serves as a cushion for the optical fiber 108 against the surfaceof the inner tube 106 to avoid microbend losses across cable bends.Suitable compounds for the filler material 114 include conventionalthixotropic gels or grease compounds commonly used in the fiber opticcable industry for water blocking, filling and lubrication of opticalfiber cables. Optionally, the filler material 114 may be omitted.

To further reduce the effects of hydrogen on the optical fibers 108, thefiller material 114 may optionally include or be impregnated with ahydrogen absorbing/scavenging material 116, such as palladium ortantalum, and the like. In one embodiment, the hydrogenabsorbing/scavenging material 116 is a vanadium-titanium wire coatedwith palladium. Alternatively, the inner tube 106 may be coated with ahydrogen absorbing/scavenging material below the barrier coating 110 oron the interior surface 118 of the inner tube 106, or such a hydrogenabsorbing/scavenging material may be impregnated into the tube material,or any combination of the above.

The optical fibers 108 are selected to provide reliable transmission ofoptical signals through the cable 100 disposed in a gas or oil wellboreapplication. Suitable optical fibers 108 include low defect, pure silicacore/depressed clad fiber. Alternatively, suitable optical fibers 108include germanium doped single mode fiber or other optical fibersuitable for use in a high temperature environment. The optical fibers108 disposed within the inner tube 106 may be comprised of the same typeor of different types of materials. Although the invention is describedherein as using three optical fibers 108 within the inner tube 106, itcontemplated that one or more fibers 108 may be used. The total numberof fibers 108 and the diameter of the inner tube 106 are selected toprovide sufficient space to prevent microbending of the optical fibers106 during handing and deployment of the cable 100.

As the fiber optic cable 100 has an operating temperature ranging atleast between about 10 to about 200 degrees Celsius, a greater length ofoptical fibers 108 are disposed per unit length of inner tube 106 toaccount for the different coefficient of thermal expansion (CTE)represented by the optical fibers 108 and the inner tube 106. The innertube diameter is configured to accept an excess length of “serpentineover-stuff” of optical fiber 108 within the inner tube 106. In oneembodiment, the excess length of optical fiber 108 may be achieved byinserting the fiber 108 while the inner tube 106 is at an elevatedtemperature, for example, during laser welding of the inner tube 106.The temperature of the inner tube 106 is controlled such that itapproximates the anticipated maximum of normal operating temperature ofthe final installation. This process will lead to an excess length offiber 108 of up to 2.0 percent or more within the inner tube 106 coolingof the inner tube.

The FIMT core 102 is surrounded by the outer tube 104 that is configuredto provide a gap 120 therebetween. The gap 120 is filled with air orother non-structural material and provides sufficient isolation betweenthe outer tube 104 and FIMT core 102 to prevent the various layers ofthe FIMT core 102 from excessively contacting the outer tube 104 andbecoming damaged. As the FIMT core 102 and outer tube 104 are notretained in continuous contact with one another, the serpentineorientation of the FIMT core 102 within the outer tube 104 (shown inFIG. 2) results in intermittent contact points 202 therebetween. Theintermittent contact points 202 retain the inner tube 106 relative tothe outer tube 104, thus creating enough friction to prevent the innertube 106 from moving within the outer tube 104 and damaging the coatingsapplied to the exterior of the inner tube 106.

Returning to FIG. 1, the outer tube 104 is manufactured of a corrosionresistant material that easily diffuses hydrogen. The outer tube 104 maybe manufactured of the same material of the inner tube 106 and may befabricated with or without a coating of a low hydrogen permeabilitycoating or hydrogen scavenging material. Examples of outer tubematerials include suitable corrosion resistant metal alloys such as, butnot limited to, 304 stainless steel, 316 stainless steel, INCONEL® 625and INCOLOY® 825, among others.

In one embodiment, the outer tube 104 is seam welded over the FIMT core106. The weld seam 124 of the outer tube 104 may be fabricated using aTIG welding process, a laser welding process, or any other suitableprocess for joining the outer tube 104 over the FIMT core 102.

After welding, the outer tube 104 is drawn down over the FIMT core 102to minimize the gap 120. The gap 120 ensures that the outer tube 104 isnot mechanically fixed to the FIMT core 102, thereby preventingthermally induced motion or strain during use at elevated temperaturesand/or over temperature cycling, which may damage the barrier and/orouter coatings 110, 112 if the outer tube 104 were to slide over theinner tube 106.

Alternatively, the outer tube 104 may be rolled or drawn down againstthe FIMT core 102, where care is taken not to extrude or stretch theFIMT core 102 such that the excess length of the fibers 108 within theFIMT core 102 is not appreciably shortened. In embodiments where theouter tube 104 and the FIMT core 102 are in substantially continuouscontact, the inner and outer tubes 106, 104 may be fabricated from thesame material to minimize differences in thermal expansion, therebyprotecting the coating applied to the exterior of the inner tube 106.

An initial diameter of the outer tube 104 should be selected withsufficient space as not to damage the FIMT core 102 during welding. Theouter tube 104 may be drawn down to a final diameter after welding. Inone embodiment, the outer tube 104 has a final diameter of less thanabout 4.7 mm to less than about 6.3 mm and has a wall thickness in therange of about 0.7 to about 1.2 mm. Other outer tube diameters arecontemplated and may be selected to provide intermittent mechanicalcontact between the inner tube 106 and the outer tube 104 to preventrelative movement therebetween.

To further protect the cable 100 during handling and installation, aprotective jacket 122 of a high strength, protective material may beapplied over the outer tube 104. For example, a jacket 122 ofethylene-chlorotrifluoroethylene (ECTFE) may be applied over the outertube 104 to aid in the handling and deployment of the cable 100. In oneembodiment, the jacket 122 may have a non-circular cross-section, forexample, ellipsoid or irregular, or polygonal, such as rectangular. Theprotective jacket 122 may be comprised of other materials, such asfluoroethylenepropylene (FEP), polyvinylidene fluoride (PVDF),polyvinylchloride (PVC), HALAR®, TEFLON®, fluoropolymer, or othersuitable material.

As the diameter of the outer tube 104 and optional protective jacket 122result in a cable 100 that is much smaller than conventional designs,more cable 100 may be stored on a spool for transport. For example, acable 100 having a diameter of about 3.2 mm may have a length of about24 kilometers stored on a single spool, thereby allowing multiplesensing systems to be fabricated from a single length of cable withoutsplicing. Furthermore, the reduced diameter of the cable 100 allows formore room within the wellhead and wellbore, thereby allowing more cables(or other equipment) to be disposed within the well. Moreover, as thecable 100 is lighter and has a tighter bending radius than conventionaldesigns, the cable 100 is easier to handle and less expensive to ship,while additionally easier to deploy efficiently down the well. Forexample, conventional quarter 6.3 mm cables typically have a bendingradius of about 101 mm, while an embodiment of the cable 100 having a3.1 mm diameter has a bending radius of less than 76.2 mm, and inanother embodiment, to about 50.8 mm.

FIG. 3A illustrates a cross sectional view of another embodiment of afiber optic cable 300 suitable for use in oil and gas wellboreapplications. The cable 300 is substantially similar in construction tothe cable 100 described above, having an FIMT core 306 disposed within aprotective outer tube 104.

The FIMT 306 comprises an inner metal tube 302 having a polymer shell304 surrounding one or more optical fibers 108. The inner tube 302 isfabricated similar to the metal embodiment of the inner tube 302described above, while the polymer shell 304 may be applied to theexterior of the inner tube 302 by extruding, spraying, dipping or othercoating method. The polymer shell 304 may be fabricated from, but is notlimited to fluoropolymers, ethylene-chlorotrifluoroethylene,fluoroethylenepropylene, polyvinylidene fluoride, polyvinylchoride,HALAR®, TEFLON® and TEFZEL®, among others. Although the polymer shell304 is illustrated as a circular ring disposed concentrically over theinner tube 302, it is contemplated that the polymer shell 304 may takeother geometric forms, such as polygonal, ellipsoid or irregular shapes.

An optional plated barrier coating (not shown) similar to the coating110 described above, may be disposed on at least one of the inner orouter surfaces of at least one of the inner tube 302 or polymer shell304. In one embodiment, a protective outer coating (also not shown)similar to the outer coating 112 described above, is disposed over thebarrier coating 110. The outer coating 112 is a protective layer ofhard, scratch resistant material, such as nickel or a polymer such aspolyamide, among others, that substantially prevents the barrier coating110 from damage from contact with the outer tube 104.

The optical fibers 108 are selected to provide reliable transmission ofoptical signals through the cable 300 disposed in a gas or oil wellboreapplication. Although the invention is described herein as using threeoptical fibers 108 within the inner tube 302, it is contemplated thatone or more fibers 108 may be used. The optical fibers 108 may bedisposed in filler material 114 that substantially fills the void spaceswithin the inner tube 302 surrounding the optical fibers 108. The fillermaterial 114 may optionally be impregnated with a hydrogenabsorbing/scavenging material 116, such as palladium or tantalum, andthe like.

The outer tube 104 is configured to intermittently contact the FIMT core306 while substantially maintain a gap 120 as described above. Theintermittent contact between the outer tube 104 and FIMT core 306prevents the FIMT core 306 from moving within the outer tube 104 whileadvantageously minimizing the outer diameter of the cable 300 ascompared to conventional designs.

FIG. 3B depicts a cross sectional view of another embodiment of a fiberoptic cable suitable for use in oil and gas wellbore applications. Thecable is substantially similar in construction to the cable 300described above, having an FIMT core 336 disposed within a protectiveouter tube 104, except that the FIMT core 336 includes a plurality offins 332.

In one embodiment, the FIMT core 336 includes an inner metal tube 302having a polymer shell 334 disposed thereover. The fins 332 extendoutwardly from the polymer shell 334. The fins 332 are typicallyunitarily formed with the shell 334 during an extrusion process, but mayalternatively be coupled to the shell 334 through other fabricationprocesses. Ends 338 of the fins 332 generally extend from the shell 334a distance configured to allow a gap 340 to be defined between the ends338 and the wall of the outer tube 104. The gap 340 allows the FIMT core336 to be disposed within the outer tube 104 in a serpentine orientation(similar to as depicted in FIG. 2), thereby allowing intermittentcontact between the FIMT core 336 and the outer tube 104 thatsubstantially secures the core 336 and outer tube 104 relative to oneanother.

In an alternative fiber optic cable 330, as depicted in FIG. 3C, theouter tube 104 may be sized or drawn down to contact the fins 332 of theFIMT core 336, thus mechanically coupling the FIMT core 336 to the outertube 104. In this embodiment, a gap 120 remains defined between theshell 334 and outer tube 104 to substantially protect the FIMT core 336and any coatings disposed thereon, while the mechanical engagement ofthe outer tube 104 and fins 332 prevent movement of the core 336 withinthe outer tube 104. Moreover, the space defined between the fins 332provides spacing between the FIMT core 336 and the outer tube 104 toprevent damage of the FIMT core 336 during welding. Additionally, thefins 332 may be slightly compressed during the reduction in diameter ofthe outer tube 104 so that the FIMT core 336 is not stretched orextruded in a manner that substantially removes the excess length offiber within the FIMT core 336.

FIG. 3D depicts a cross sectional view of another embodiment of a fiberoptic cable 350 suitable for use in oil and gas wellbore applications.The cable 350 is substantially similar in construction to the cable 330described above, having a fiber in tube (FIT) core 356 disposed within aprotective outer tube 104, except that the FIT core 356 includes aplurality of fins 352 extending from a polymer inner tube 354 thatsurrounds at least one optical fiber 108 without an intervening metaltube.

The fins 352 are unitarily formed with the polymer inner tube 354 duringan extrusion process, but may alternatively be coupled to the inner tube354 through other fabrication processes. During fabrication, the opticalfiber 108 is disposed in the polymer inner tube 354 while the tube 354is in an expanded state, for example, immediately after the polymerinner tube 354 is extruded or after heating the tube. As the polymertube 354 cools and shrinks, the length of optical fiber 108 per unitlength of polymer tube 354 increases, thereby allowing enough opticalfiber 108 to be disposed within the polymer tube 354 to ensure minimalstress upon the optical fiber 108 after the polymer tube 354 hasexpanded when subjected to the hot environments within the well.

Ends 358 of the fins 352 generally extend from the polymer inner tube354 a distance configured to allow a gap to be defined between the ends358 and the wall of the outer tube 104 or to contact the outer wall 104as shown. In either embodiment, a gap 120 remains defined between thepolymer inner tube 354 and outer tube 104 to substantially protect theFIT core 356 and any coatings disposed thereon.

FIG. 3E depicts a cross sectional view of another embodiment of a fiberoptic cable 360 suitable for use in oil and gas wellbore applications.The cable 360 is substantially similar in construction to the cable 350described above, having a FIT core 366 disposed within a protectiveouter tube 104, except that the FIT core 366 defines a polymer withoutfins and without an intervening metal tube.

The FIT core 366 has a polygonal form, such as a triangle or polygon (asquare is shown in the embodiment depicted in FIG. 3E). However, it iscontemplated that the FIT core 366 may take other geometric forms, suchas polygonal, ellipsoid, circular or irregular shapes, where the FITcore 366 has a different geometric shape than the inner diameter of theouter tube 104.

In the embodiment depicted in FIG. 3E, the FIT core 366 includes corners368 that generally extend from the FIT core 366 a distance configured toallow a gap to be defined between the corners 368 and the wall of theouter tube 104 or to contact the outer wall 104 as shown. In eitherembodiment, a gap 120 remains defined between the FIT core 366 and outertube 104 to substantially protect the FIT core 366 and any coatingsdisposed thereon.

FIG. 4 depicts another embodiment of a cross sectional view of anotherembodiment of a fiber optic cable 400 suitable for use in oil and gaswellbore applications. The cable 400 is substantially similar inconstruction to the cables described above, except that the cable 400includes an expanded polymer spacer 402 that applies a force against anouter tube 104 and an FIMT core 102 that bound the spacer 402.

The polymer spacer 402 may be a foamed polymer, such as urethane orpolypropylene. In one embodiment, the polymer spacer 402 may be injectedand foamed between the outer tube 104 and the FIMT core 102 after theouter tube 104 has been welded. In another embodiment, the polymerspacer 402 may be disposed over the FIMT core 102 and compressed duringa diameter reducing step applied to the outer tube 104 after thewelding. In yet another embodiment, the polymer spacer 402 may beapplied to the exterior of the FIMT core 102, and activated to expandbetween the outer tube 104 and the FIMT core 102 after welding. Forexample, the polymer spacer 402 may be heated by passing the cable 400through an induction coil, where the heat generated by the inductioncoil causes the polymer spacer 402 to expand and fill the interstitialspace between the outer tube 104 and the FIMT core 102. As the polymerspacer 402 is biased against both the outer tube 104 and the FIMT core102, any well fluids that may breach the outer tube 104 are preventedfrom traveling along the length of the cable 400 between the outer tube104 and the FIMT core 102.

FIGS. 5-6 are a flow diagram and simplified schematic of one embodimentof a method 500 for fabricating the optic cable 330. The reader isencouraged to refer to FIGS. 5 and 6 simultaneously.

The method 500 begins at step 502 by extruding a polymer tube 602through a die 620 around at least one or more optical fibers 604. Theoptical fibers 604 may optionally be sheathed in a seam welded metaltube as described with reference to FIG. 1, and as described in U.S.Pat. No. 6,404,961, incorporated by reference. As the polymer tube 602is formed, the one or more optical fibers 604 are deployed from a firstconduit or needle 612 extending through the die 620 into the tube 602 toa point downstream from the extruder 606 where the polymer comprisingthe tube 602 has sufficiently cooled to prevent sticking of the fibers604 to the tube wall at step 504. The one or more optical fibers 604 aredisposed in the tube 602 at a rate slightly greater than the rate oftube formation to ensure a greater length of optical fiber 604 per unitlength of polymer tube 602.

At an optional step 506, a filler material 608 may be injected into theinterior of the polymer tube 602 to fill the void spaces surrounding theoptical fibers 604. The filler material 608 is injected from a secondconduit or needle 610 extending through the die 620 of the polymer tube602 to a suitable distance beyond the extruder to minimize any reactionbetween the cooling polymer tube 602 and the filler material 608. Thefiller material 608 may optionally be intermixed with a hydrogenabsorbing/scavenging material.

At an optional step 508, the polymer tube 602 may be coated with abarrier material 614. The barrier material may be applied by plating,passing the tube 602 through a bath, spraying and the like. In oneembodiment, the barrier material 614 is plated on the polymer tube 602by passing the tube through one or more plating baths 618.

At an optional step 510, a protective outer sleeve 624 is formed aroundthe polymer tube 602. The outer sleeve 624 may include seam welding ametal strip 626 to form the sleeve 624 around the polymer tube 602. Theprotective outer sleeve 624 may also include a polymer jacket 628applied over the sleeve 624. The polymer jacket 628 may be formed byspraying or immersing the sleeve 624 in a polymer bath after welding. Ifa protective outer sleeve 624 is disposed over the polymer tube 602, themetal sleeve 624 may be drawn down into continuous contact with thepolymer tube 602 at step 512.

Thus, a fiber optic cable suitable for use in harsh environments such asoil and gas wellbore applications has been provided. The novel opticcable has unique construction that advantageously minimizes fabricationcosts. Moreover, as the novel optic cable has a reduced diameter thatallows greater spooled lengths of cable facilitates more efficientutilization as compared to conventional cable designs, therebyminimizing the cost of optical sensing systems that utilize optic cablesin oil field applications.

FIG. 8 shows a cross sectional diagrammatic view of a wellbore 800 withthe fiber optic cable 350 shown in FIG. 3D disposed in the wellbore 800.The cable 350 couples to a flow control device, such as a pump 802and/or valve, for circulating fluid within the cable 350. The pump 802receives the fluid from a source 804 for inputting the fluid into thecable 350 as depicted by an arrow indicating flow 806. For someembodiments, the fluid in the source 804 may be pressurized such that noadditional pumping of the fluid is required. The source 804 holds orotherwise provides the fluid, which may be a liquid or gas selected suchthat circulation of the fluid through the cable 350 flushes awayhydrogen that may be diffusing into the cable 350.

A termination 808 of the cable 350 includes either a cross-over area forflowing the fluid back through other flow paths of the cable 350 asdescribed further herein or a vent, which may include a one-way valveassembly to let the fluid escape into the wellbore 800 withoutpermitting ingress into the cable 350. Returning the fluid back tosurface for discharge avoids potential complications of introducing thefluid in the wellbore, such as subsequent separation and removal of thefluid from other wellbore fluids or possible fluid locks created by thetermination 808 being in a trapped volume, and facilitates ensuring nobreach of the cable 350 in the wellbore 800 as may occur with problemsfrom venting in the wellbore 800. One way flow of the fluid through thecable 350 thus may offer a more desirable approach in other applicationswhere the cable 350 is not deployed in the wellbore 800.

FIG. 9 illustrates an enlarged sectional view taken at 9 in FIG. 8. Theflow 806 of the fluid traverses along a length of the cable 350 througha first path 119 defined by one of the gaps 120 between the inner andouter tubes 354, 104 of the cable 350. The first path 119 retains theflow 806 of the fluid in at least part of an annular area around theinner tube 354 surrounding the optical fibers 108 of the cable 350.Referring to FIG. 3D, the fins 352 may isolate the first path 119 formedby one of the gaps 120 from one or more other circumferential spacedones of the gaps 120. Another one of the gaps 120, for example, may forma second path 121 separate from the first path 119. In operation, thefluid may flow through the second path 121 in an opposite direction fromthe flow 806 of the fluid in the first path 119 to enable return of thefluid upon reaching the termination 808 (shown in FIG. 8). As with otherembodiments described herein, the termination 808 may include apertures,such as through the fins 352, or spacing between components at endswhere, for example, at least the fins 352 terminate prior to reaching anenclosing end face of the cable 350. Such exemplary arrangements at thetermination 808 enable flow to cross-over from the first path 119 to thesecond path 120. The flow 806 of the fluid may occur through any or allof the gaps 120. For some embodiments such as those where venting occursat the termination 808, the flow 806 of the fluid passes in onedirection around the inner tube 354 making isolation between the firstand second paths 119, 121 not required as shown by example in FIG. 3B.

Regardless of configuration, the fluid may circulate through the cable350 between first and second terminal ends of the cable 350. Thecirculation occurs for a period of time as required for removal ofhydrogen during life of the cable 350, such as longer than one of a day,a week and a month. To provide the flow 806 across a desired length ofthe cable 350, the fluid enters and exits the cable 350 via an inlet andoutlet at selected locations, such as proximate one of the ends of thecable 350 or respectively at each end of the cable 350 if no return ofthe fluid is desired. The inlet and outlet being defined makescontrolled fluid flow through the first and second paths 119, 121possible.

Operations to remove hydrogen utilize controlled circulation of thefluid through the cable 350. For some embodiments, sizing of the firstand second paths 119, 121, pressure of the fluid in the source 804,and/or operation of the flow control device such as the pump 802 or avalve at where the flow 806 exits the cable 350 controls the flow 806 ofthe fluid into the cable 350. For some embodiments, flow rate of thefluid through the cable 350 may provide an exchange rate of all thefluid within the cable 350 of about once per day. This exchange rate maycorrespond to the flow rate being between 0.05 cubic meters and 1.5cubic meters per day, as the cable 350 may contain less than about 0.03cubic meters of fluid per 3000 meters of the cable 350. In someembodiments, the flow 806 of the fluid may occur in intermittent pulsesinstead of a continuous flow to conserve the fluid.

In some embodiments, the source 804 includes the fluid that may be amixture and that may be non-hydrogen containing. As size of the paths119, 121 in the cable 350 through which the fluid is flowing decreases,liquids become more difficult to circulate making gases more desirablein some applications. Exemplary gases for the fluid in the source 804include air, nitrogen, helium, fluorine, argon, oxygen, neon, krypton,xenon, radon, carbon monoxide, carbon dioxide and mixtures thereof.Further, the fluid from the source 804 may contain hydrogen scavengingcompounds such as fullerenes including buckminsterfullerenes, carbontetrachloride, perfluorohexane, potassium iodate and mixtures thereof.

FIG. 10 shows a cross sectional view of the fiber optic cable 330 asshown in FIG. 3C with addition of first and second flow tubes 900, 901between the inner and outer tubes 302, 104. While two of the flow tubes900, 901 are shown, the cable 330 may include any number of the flowtubes 900, 901. As described with reference to FIG. 8, flowing of fluidthrough one or more of the flow tubes 900, 901 and returning the fluidthrough the gap 120 flushes hydrogen from within the cable 330 prior tothe hydrogen reaching the optical fibers 108. The flow tubes 900, 901can withstand pressures necessary to establish circulation of the fluid.Passing the fluid inside the flow tubes 900, 901 facilitates in ensuringthat a distinct and stable flow path extends across all of the cable 330prior to the fluid being returned back through the cable 330.

FIG. 11 illustrates a cross sectional view of a fiber optic cable with afiller body 910 disposed between inner and outer tubes 102, 104 in aspaced relationship with both the inner and outer tubes 102, 104. In oneembodiment, aluminum that may be extruded over or wrapped and weldedaround the inner tube 102 forms the filler body 910. In someembodiments, the inner tube 102 may be concentric with the outer tube104 and may be made of metal. Separation between the filler body 910 andthe outer tube 104 creates an outer annular flow path 911 concentricwith an inner annular flow path 912 provided by spacing between theinner tube 102 and the filler body 910. The filler body 910 isolates theannular flow paths 911, 912 from one another until cross-over isdesired. In some embodiments, an outer diameter of the filler body 910being about 0.1 to 0.3 mm smaller than an inner diameter of the outertube 104 and an outer diameter of the inner tube 102 being about 0.1 to0.3 mm smaller than an inner diameter of the filler body 910 establishthe annular flow paths 911, 912.

FIG. 12 shows a cross sectional view of the fiber optic cable shown inFIG. 11 taken across line 12-12. Referring again to FIG. 8, fluid flowthrough the annular flow paths 911, 912 removes any hydrogen thatpermeates through the outer tube 104 to reduce or eliminate impact ofhydrogen on optical fibers 108 contained in the inner tube 102.Pressurization and return of the fluid can occur respectively througheither of the annular flow paths 911, 912. For example, input flow 921may pass through the outer annular flow path 911 for a cable lengthprior to being returned through the inner annular flow path 912 asdepicted by return flow 922. The input and return flows 921, 922 asdepicted, respectively enter and exit the outer and inner annular flowpaths 911, 912, thereby illustrating, for example, the inlet and theoutlet.

FIG. 13 illustrates a cross sectional view of a fiber optic cable havingan outer tube 104 surrounding a filler body 930, first and second flowtubes 932, 933 embedded in the filler body 930, and an inner tube 102also embedded in the filler body 930 with fibers 108 inside the innertube 102. For some embodiments, extrusion of aluminum over the innertube 102 and the flow tubes 932, 933 forms the filler body 930.Centralization of the inner tube 102 within the filler body 930 preventslength mismatch between the inner and outer tubes 102, 104 as a resultof coiling or uncoiling. Pressurization of the flow tubes 932, 933 withfluid at a first end of the flow tubes 932, 933 passes the fluid to asecond end of the flow tubes 932, 933 where the fluid exiting the secondend of the flow tubes 932, 933 is directed back along an annulus 931between the filler body 930 and the outer tube 104. A gap between anouter diameter of the filler body and an inner diameter of the outertube 104 creates the annulus 931, which is purged of hydrogen by thefluid that is circulated therein.

FIG. 14 shows a cross sectional view of a fiber optic cable formed by anouter tube 104 surrounding first and second flow tubes 941, 942 strandedor twisted together with an inner tube 940 that has optical fibers 108inside. The flow tubes 941, 942 and inner tube 940 for some embodimentsinclude a coating to hold the flow tubes 941, 942 and inner tube 940together. Gaps 120 of open space exist external to the flow tubes 941,942 and inner tube 940 and inside of the outer tube 104. Like otherembodiments described herein, flowing fluid through the flow tubes 941,942 in a first direction along a cable length and then flowing the fluidback through the gaps 120 along the cable length in a second directionthat is opposite the first direction flushes away any hydrogen gas thathas migrated through the outer tube 104 before the hydrogen gas canbuild a partial pressure enough to penetrate the inner tube 102containing the optical fibers 108.

Compared to designs that introduce a gas barrier in direct contact withoptical fibers, embodiments of the invention provide several advantages.For example, the gas barrier in direct contact with the optical fibersrequires leaving the fibers in an unsupported condition and subject tofree movement. Further, purging hydrogen at the optical fiber itselfmeans that any hydrogen in flow for the gas barrier can interact withthe optical fiber as there is nothing blocking the hydrogen from accessto the fibers. Redundant hydrogen barriers or hydrogen scavengingtechniques on the other hand can benefit from reduced hydrogenconcentrations when hydrogen is purged ahead of such redundant hydrogenbarriers. Moreover, integration of purging fluid inflow and outflow in asingle cable facilitates deployment of the cable. Another exemplaryadvantage provided by embodiments of the invention includes ability toincorporate various cable design aspects in which optical fibers aredisposed without being limited to running of bare optical fibers withinthe gas barrier.

Based on the foregoing, various arrangements exist for providing one ormore flow paths in a cable between an inner tube containing opticalfibers and an outer tube surrounding the inner tube. The flow pathsenable flowing of fluid to prevent hydrogen ingress to the opticalfibers as exemplarily illustrated for various embodiments herein eventhough other configurations, such as shown in FIG. 1, may providesuitable flow paths. Although the invention has been described andillustrated with respect to exemplary embodiments thereof, the foregoingand various other additions and omissions may be made therein andthereto without departing from the spirit and scope of the presentinvention.

1. An optic cable comprising an outer tube; an inner tube disposedinside the outer tube, wherein a flow path is disposed between the innerand outer tubes, extends along a length of the cable, and includes aninlet and an outlet, the flow path for controlling flow of a fluid toremove hydrogen from the cable, wherein the outer tube has an innerdiameter sized for relative retention of the inner tube; an opticalfiber disposed inside the inner tube; and at least one flow tubedisposed inside the outer tube, wherein the flow path includes aninterior of the flow tube.
 2. The optic cable of claim 1, wherein theinlet introduces the fluid into the flow tube and the outlet receivesthe fluid introduced at the inlet and returned via a gap between aninterior of the outer tube and exteriors of the inner and flow tubes. 3.The optic cable of claim 1, wherein the at least one flow tube isstranded or twisted together with the inner tube.
 4. The optic cable ofclaim 1, further comprising a filler body disposed inside the outertube, wherein the inner and flow tubes are embedded in the filler bodyand wherein the gap comprises an annular path between the interior ofthe outer tube and an exterior of the filler body.
 5. The optic cable ofclaim 4, wherein the filler body comprises a tubular aluminum body. 6.The optic cable of claim 4, wherein the inner tube is centered withinthe filler body.
 7. The optic cable of claim 1, wherein the gapcomprises spaces between a plurality of fins disposed between theinterior of the outer tube and the exterior of the inner tube and the atleast one flow tube is disposed in at least one of the spaces.
 8. Theoptic cable of claim 7, wherein the inner tube is surrounded by apolymer shell and the plurality of fins extend outwardly from thepolymer shell.
 9. The optic cable of claim 7, wherein ends of theplurality of fins contact the interior of the outer tube.
 10. An opticcable comprising: an outer tube; an inner tube disposed inside the outertube, wherein a flow path is disposed between the inner and outer tubes,extends along a length of the cable, and includes an inlet and anoutlet, the flow path for controlling flow of a fluid to remove hydrogenfrom the cable, wherein the outer tube has an inner diameter sized forrelative retention of the inner tube; and an optical fiber disposedinside the inner tube, wherein the flow path comprises first and secondannular paths coextensive along the length of the cable, but separatedalong part of the length from one another, the inlet configured tointroduce the fluid into the first annular path and the outletconfigured to receive the fluid exiting the cable from the secondannular path.
 11. The optic cable of claim 10, wherein a tubularaluminum body disposed between the inner and outer tubes is sized toform the annular paths between the aluminum body and the inner tube andbetween the aluminum body and the outer tube.
 12. An optic cable system,comprising: a cable comprising: an outer tube; at least one flow tubedisposed inside the outer tube; an inner tube disposed inside the outertube, wherein a flow path disposed between the inner and outer tubesextends across a length of the cable and includes an inlet, an outlet,and an interior of the flow tube; and an optical fiber disposed insidethe inner tube; and a source of fluid coupled to the inlet of the flowpath, wherein the inlet introduces the fluid from the source into theflow tube and the outlet receives the fluid introduced at the inlet andreturned via a gap between an interior of the outer tube and exteriorsof the inner and flow tubes.
 13. The optic cable system of claim 12,wherein the fluid is pressurized to achieve controlled fluid flow of thefluid through the flow path from the inlet toward the outlet, thecontrolled fluid flow to remove hydrogen from within the cable.
 14. Theoptic cable system of claim 12, further comprising a filler bodydisposed inside the outer tube, wherein the inner and flow tubes areembedded in the filler body and wherein the gap comprises an annularpath between the interior of the outer tube and an exterior of thefiller body.
 15. The optic cable system of claim 12, wherein the gapcomprises spaces between a plurality of fins disposed between theinterior of the outer tube and the exterior of the inner tube andwherein the at least one flow tube is disposed within at least one ofthe spaces.
 16. The optic cable system of claim 12, wherein the fluidcomprises at least one of air, nitrogen, helium, fluorine, argon,oxygen, neon, krypton, xenon, radon, carbon monoxide, carbon dioxide,and mixtures thereof.
 17. The optic cable system of claim 12, whereinthe fluid comprises hydrogen scavenging compounds.
 18. The optic cablesystem of claim 12, wherein the fluid comprises one of a fullerene,carbon tetrachloride, perfluorohexane, potassium iodate, and mixturesthereof.
 19. An optic cable comprising: an outer tube; an inner tubedisposed inside the outer tube, wherein a flow path is disposed betweenthe inner and outer tubes, extends along a length of the cable, andincludes an inlet and an outlet, the flow path for controlling flow of afluid to remove hydrogen from the cable; at least one flow tube disposedinside the outer tube, wherein the flow path includes an interior of theflow tube; and an optical fiber disposed inside the inner tube.